The present invention relates to a process and to a device for the automatic identification of increased resonance response during the balancing procedure on permanently calibrated, hard-bearing balancing machines.
Rotors to be balanced on balancing machines constitute a vibratory system consisting of various masses and different degrees of stiffness. For a precise determination of the unbalance values, permanently calibrated, hard-bearing balancing machines require that the unbalance values not be measured in vicinity of the resonance speeds, since this greatly increases the measuring errors. For this reason, the unbalance is usually measured in a rotational speed range which is approximately 30% of the first resonance speed. In this process, the resonance speed is largely determined by the magnitude of the rotor mass, the rotor moment of inertia, the masses of the bearings as well as the stiffness of the rotor and bearings of the system consisting of rotor and balancing machine.
Until now, the maximum permissible balancing speed for permanently calibrated, hard-bearing balancing machines was calculated by means of tables. For this purpose, the operator of the balancing machine could read the maximum permissible balancing speed for the rotor weight in question from a table provided by the manufacturer. In general, these tables containing the speed data only provided the maximum permissible balancing speeds which were valid for symmetrical rotors. Only one vibration mode was taken into consideration; namely, parallel displacement of a rigid rotor in flexible bearings. In the case of hard-bearing, permanently calibrated balancing machines, in addition to the above-mentioned mode, it is usually necessary to also take into consideration two other vibration modes whose appertaining resonance speeds can sometimes be below the resonance speed of the parallel displacement mode of the rotor. These two vibration modes presume the counter movement of a relatively rigid rotor in flexible bearings on the one hand, and the bending of a flexible rotor in relatively rigid bearing supports on the other hand.
Which resonance speed is the smallest for a certain rotor-bearing system depends on the rotor mass and on its moments of inertia, on the masses of the bearings and on the stiffness of the rotor and bearings. As a rule, the resonance speed of a vibration mode whose speed is the lowest determines the limit of the permanent calibraton and the plane separation based on the geometry of the rotor. In this case, the rules of the single-mass spring system should be employed as an approximation, since this is the mode that predominates.
For this reason, when taking into consideration only the vibration mode for the parallel displacement of a rigid rotor with relatively flexible bearings, it is sometimes the case that the maximum permissible balancing speeds--which have been ascertained from the tables for the rotor to be balanced--are selected excessively high, thus leading to increased resonance responses, which distort the measured results without the operator realizing it.